This section provides background information related to the present disclosure which is not necessarily prior art.
In view of consumer demand for 4WD and AWD motor vehicles, a large number of power transfer systems are currently utilized in vehicular applications for selectively and/or automatically transmitting rotary power (i.e., drive torque) from the powertrain to all four wheels. In most power transfer systems, a power transfer assembly is used to deliver drive torque from the powertrain to one or both of the primary and secondary drivelines. The power transfer assembly is typically equipped with a torque transfer clutch that can be selectively actuated to shift operation of the power transfer system between a two-wheel drive mode and a four-wheel drive mode. In the two-wheel drive mode, drive torque is only transmitted from the powertrain to the primary driveline. In contrast, a portion of the drive torque generated by the powertrain can also be transmitted through the torque transfer clutch to the secondary driveline when the vehicle is operating in the four-wheel drive mode.
In most 4WD vehicles, the power transfer assembly is a transfer case arranged to normally transmit drive torque to the rear driveline and selectively/automatically transfer drive torque through the torque transfer clutch to the front driveline. In contrast, in most AWD vehicles, the power transfer assembly is a power take-off unit (PTU) arranged to normally transmit drive torque to the front driveline and selectively/automatically transfer drive torque through the torque transfer clutch to the rear driveline.
Many power transfer assemblies are equipped with an adaptively-controlled torque transfer clutch to provide an “on-demand” power transfer system operable for automatically biasing the torque distribution ratio between the primary and secondary drivelines, without any input or action on the part of the vehicle operator, when traction is lost at the primary wheels. Modernly, such torque transfer clutches are configured to include a multi-plate friction clutch and a power-operated clutch actuator that is interactively associated with an electronic traction control system having a controller and a plurality of vehicle sensors. During normal operation, the friction clutch can be maintained in a released condition so as to transmit drive torque only to the primary wheels and establish the two-wheel drive mode. However, upon detection of conditions indicative of a low traction condition, the power-operated clutch actuator is actuated to engage the friction clutch and deliver a portion of the total drive torque to the secondary wheels, thereby establishing the four-wheel drive mode.
In virtually all power transfer systems of the types noted above, the secondary driveline is configured to include a propshaft, a drive axle assembly, and one or more constant velocity universal joints. The opposite ends of the propshaft are drivingly interconnected via the constant velocity joints to a rotary output component of the power transfer assembly and to a rotary input component of the axle assembly. Typically, a hypoid gearset is used to transmit drive torque from the propshaft to a differential gear mechanism associated with the drive axle assembly. The differential gear mechanism may include a differential carrier rotatably supported in an axle housing and which drives at least one pair of bevel pinions which, in turn, are commonly meshed with first and second output bevel gears that are connected to corresponding first and second axleshafts which drive the secondary wheels. The hypoid gearset typically includes a pinion gear meshed with a ring gear. The pinion gear is typically formed integrally with, or fixed to, a solid pinion shaft that is rotatably support by the axle housing. The pinion shaft is usually connected via one of the constant velocity joints to the propshaft. The ring gear is usually fixed for rotation with the differential carrier. Due to the axial thrust loads transmitted through the hypoid gearset, it is common to utilize at least two laterally-spaced tapered bearing assemblies to support the pinion shaft for rotation within the axle housing.
Many constant velocity joints (CVJ) are sealed in order to retain a lubricant, such as grease, inside the joint while keeping contaminants and foreign matter, such as dirt and water, out of the joint. To achieve this protection, the CVJ is typically enclosed at the open end of the outer race by a sealing boot made of resilient and flexible material, such as rubber. The opposite end of the outer race is sometimes formed by an enclosed dome or grease cap. Such sealing is necessary since once the inner chamber of the CVJ is partially-filled with the lubricant, it is generally lubricated for life. It is often necessary to vent the CVJ in order to minimize air pressure fluctuations which result from expansion and contraction of air within the joint during operation and as a result of elevation changes.
In addition to fixed constant velocity joints, plunging constant velocity joints are also used in 4WD and AWD vehicles to provide a plunging end motion feature which allows the interconnected shafts to change length during operation. Plunging constant velocity joints are commonly used to interconnect the pinion shaft of the hypoid gearset in the drive axle assembly to the propshaft. One type of plunging constant velocity joint includes a plurality of balls retained in a cage and which are located in circumferentially-spaced straight or helical grooves formed in the inner and outer races. Typically, the outer race of the CVJ is fixed to the propshaft stub shaft which, in turn, is fixed to the propshaft tube section. An intermediate flange component is then required to attach the differential end of the CVJ to a traditional pinion shaft. This standard design tends to increase the overall system length of the driveline arrangement and results in increased weight.
While such conventional coupling arrangements between the propshaft and the pinion shaft of the power transfer assembly are adequate for their intended purpose, a need still exists to advance the technology and structure of such products to provide enhanced configurations that provide improved efficiency, reduced weight, and reduced packaging requirements.